1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display having improved screen quality by preventing abnormal light leakage due to ions in a pixel.
2. Description of the Related Art
Compared with Cathode-Ray Tube (hereinafter, referred to as “CRT”), a Liquid Crystal Display (hereinafter, referred to as “LCD”) generally has advantages of lightweight, thin structure and low power consumption and therefore, it has been substituted for the CRT in a terminal of information apparatus and video devices. Recently, a LCD having a Thin Film Transistor (hereinafter, referred to as “TFT”) as a switching device in each pixel arranged in a shape of matrix has realized a wide viewing angle, thereby preventing a color shift and obtaining a high quality screen. As a result, the TFT-LCD has been widely used as a monitor of laptop and desktop computers and as a TV screen.
Generally, the LCD comprises an array substrate having a structure that a TFT and a pixel electrode are formed in a pixel, a color filter substrate including a color filter and a counter electrode and a liquid crystal layer interposed between the substrates. The LCD realizes a predetermined image by driving liquid crystal molecules according to the voltage applied to the pixel electrode and the counter electrode.
FIG. 1 is a top plan view showing a pixel structure in a conventional LCD. As shown in the drawing, a plurality of gate lines 2 are arranged to be perpendicular to a plurality of data lines 4. A gate insulating layer (not shown) is interposed between them for electrical insulation thereof.
A TFT 10 is formed at the intersection of the gate line 2 and the data line 4 to control driving of each pixel. The TFT 10 includes a gate electrode forming a part of the gate line 2, a semiconductor layer (not shown) formed in a shape of pattern on the gate electrode and a source and a drain electrodes 4a and 4b formed to be overlapped with a part of the semiconductor layer. The source electrode 4a is in a shape of island and the drain electrode 4b is extended from the data line 4.
A protective layer (not shown) is formed on the resulting surface. A pixel electrode 6 made of transparent metal such as Indium Tin Oxide (ITO) is formed in a pixel region defined by the gate line 2 and the data line 4 to be in contact with the source electrode 4a. The pixel electrode 6 is formed in a rectangular shape, thereby forming the same electric field by the same voltage in the whole pixel region.
A color filter substrate is arranged opposite to the array substrate on the upper part thereof. The color filter substrate comprises a red, a green and a blue color filters (not shown) formed corresponding to pixels of the array substrate, respectively, a block matrix 12 formed on the interface of pixels, that is, on the upper part of the gate line 2 and the data line 4, and a counter electrode (not shown) formed on the whole region including the color filter and the black matrix 12.
Although it is not shown in the drawing, a plurality of liquid crystal molecules is interposed between the array substrate and the color filter substrate.
However, the conventional LCD has a problem that a screen quality is lowered due to abnormal light leakage such as afterimage by distorted data signal voltage since ions in the LCD prevent the application of desirable voltage.
That is, during the manufacturing process, ions are added to the LCD that contains ions originally. And, the pixel electrode of the array substrate and the counter electrode of the color filter substrate are formed in a rectangular shape so that there is no region generating more intensive electric field by the same voltage in the whole pixel region.
In this case, when the data signal voltage is applied, ions in the pixel are uniformly adsorbed in the pixel by DC component voltage and then, liquid crystals in the pixel receive a voltage different from the data signal voltage applied by the ions adsorbed in the pixel. As a result, undesirable movements of liquid crystals are caused, thereby generating abnormal light leakage such as an afterimage.